Check my theory

[Gina D.]

LONG POST!!! GEEKS WILL LOVE IT...

Some of you who attended the So. Cal mountain ranch rally are familiar with my gray water tank filling woes. Many members spent many hours playing a twister game in my rig plugging as many drains as possible to find out where my plumbing might be blocking my vent stack. Every time I tried to drain a kitchen sink full of water all at once, the water would back up into the shower... the lowest drain in the rig. Note that this was boondocking, so I was using my tank exclusively, no sewer hook up.

I could get the pipes to drain easily by opening the gray valve and letting it drain onto the ground or into a blue boy, OR by unleveling the trailer so it was nose down. Seemed weird.

We gave up after backflushing the vent tube. We could fill my tank to the point of it actually overflowing out the top of the vent tube, which is 7 feet tall and comes out the roof. Figured if that much water was coming out, air had to be getting in.

A kind user here with the same trailer pointed out that he had the same issue and discovered that is was the way the pipe going into the gray tank from the kitchen drains was canted. Sure enough, the pipe runs UPHILL when the trailer is level and a sudden influx of water collects in a short run elbow and blocks the vent. This elbow is located to the left and down as you look into the cubby under the sink.

OK, I have temporarily solved the problem by *slowly* draining the sink..its been 3 years now...and I finally got around to fixing the cant on the pipe. I simply cut about 2 inches out of the vent pipe below where the sink drain pipes joins the vent, raised the lower plumbing up so its canted towards the nose of the rig and down to the tank.. problem solved.

What problem is there now, you ask.. wishing I would get this over with...

[Gina D.]

My gray tank has a MUCH larger capacity than I thought it had. About 5 gallons more by my edjumicated estimate. 15 total instead of 10.. maybe a few oz more.

I drained the gray water tank BEFORE I fixed the pipe, into a sewer hook up. Before, if I had the trailer leveled *just right* to fix the cant, I could get 10 gallons into the tank without any back flow. When the gurgling and back up happened, it happened anytime, not just with a kitchen sink rush.. it did it with the shower or bathroom sink too.. so I assumed the tank was full. When this happened, I could get 2 5 gallon blue boys full with no more coming out. SOO.. I assumed the tank was ten gallons.

Fast forward to my plumbing tests today. After adjusting the pipes, I filled and quick drained the sink many times to test. No backflow (Yay!) When the backflow started, I had done 5 sinkfulls, at an estimated 2.5 - 3 gallons each. This would make sense given a couple gallons in the pipes and vent itself.

I went to drain the gray tank. I got:

2 6 gallon totes and one 5 gallon tote. Thats 17 gallons! I have never gotten that much out before.. Where did the extra come from?

My theory is that because the pipe was canted "backwards" even tho I could get a flow sometimes, that when the tank reached 10 gallons it was trickle backflowing into the pipe and draining back DOWN to the elbow, blocking the vent.

Any other ideas?

[Scott H]

So I'm a new RV'er and don't get it. My gray water is only out of the kitchen sink; ecosafe soap, and food particicles. I strain the output depending on the sensitivity of the area I'm camped (nylon, or metal mesh). Being a backpacker, and a river nut I figured that these sensibilities would be adequate. Please school me!

[Gina D.]

Scott, I have a holding tank that is fed by my kitchen sinks, my shower, and a bathroom sink. Most trailer over 13 foot are similar.

Most places frown on dumping gray water onto the ground, strained or not. The tanks hold the water and then you dump it into a sewer directly, or into a container to take to a sewer or toilet for disposal.

I have been known to release small amounts of gray into the firepit, but dumping a whole tank all at once would definately have an impact on the ground, clean or no.

I was a backpacker at one time as well and did as you do, but a trailer has a slightly larger impact.

[Frederick L. Simson]

My theory is that because the pipe was canted "backwards" even tho I could get a flow sometimes, that when the tank reached 10 gallons it was trickle backflowing into the pipe and draining back DOWN to the elbow, blocking the vent.

Any other ideas?

Words aren't doing it for me... can you draw a before diagram and an after diagram?

[Gina D.]

okey dokey.. hold on

[Gina D.]

my mouse batteries died making it impossible to do graphics.

water will not flow uphill without help. Pipe is going uphill to tank. Water collects at intersection where vent tube goes up at ninety degrees, blocking the vent because at that point, the drain is going DOWN, and UP to the tank. Gray tank full of air, water can not go in so it finds the lowest point, path of least resistance. The shower drain pipe, which is canted correctly.

Even if vent isn't blocked, water rises in tank, finds the bottom of the outflow pipe and water flows back DOWN it and blocks the intersection, because the pipe is pointed DOWN at that point. Water flows downhill willingly.

Without that "Back drain", it could easily account for the extra gallons.

I think.

[Per Walthinsen]

The thoroughly competent and utterly reliable guys at Burro state in the owner's manual that the gray water tank is indeed 17 gallons. (Reagan: trust but verify, so I did, and it came to 17 gallons all right.) Have not had any backflow problems, so I'm no help at all. The verify thing will not be repeated for the blackwater tank, at least not in my lifetime.

[Gina D.]

Thanks Per. My manual got wet and is now a blur of 90s era cheap printing ink. Can't read a word.

I don't remember what it said when I first read it. I DO remember that they were ambiguous about the black "Either 8 or 10" gallons. Mine is 8.. I have verified, unfortunately.

[pjanits]

Thanks Per. My manual got wet and is now a blur of 90s era cheap printing ink. Can't read a word.

I don't remember what it said when I first read it. I DO remember that they were ambiguous about the black "Either 8 or 10" gallons. Mine is 8.. I have verified, unfortunately.

OY!

Good deductions and corrections Gina.

[Phil Underwood]

did you happen to take any pics of this new mod ?

[Raya]

It's hard to be super definitive without seeing photos or a diagram, but if I understand what you're saying correctly, your theory makes sense to me. Vents can wreak a bit of havoc if they aren't happy

How nice to find that you have an additional 50% of tank capacity! It's like me waking up and finding that I have a 21-footer

[Lizbeth]

All I have to say about this is YEA!